The present invention relates to the manufacture of reinforced structures for parts of composite material, and more particularly for wheels, rims or rim elements.
Numerous methods exist for producing wheels or rims of composite material. Mention may be made, in particular, of high-precision injection molding of reinforced thermoplastic resins or of compression molding of thermosetting resins which are also reinforced.
These techniques require the use of staple fibers, which result in average mechanical properties of the finished products as well as their difficult mechanical optimization due to the displacements of the reinforcement fibers during the molding.
If it is desired to use continuous fibers, one can select an existing fabric. More industrially, one can also select the method of manufacturing composite parts known as R.T.M. (resin transfer molding) or any derivative process. In this process, the reinforcement materials, such as glass fibers, carbon fibers or fibers of any other type, are prearranged in the cavity of a mold. These reinforcement materials thus form the "preform" of the final composite part. This operation of putting in place and structuring the reinforcements is known as "preforming". The resin is then transferred through the preform into the mold under vacuum and/or with a transfer pressure, and then cross-linked at suitable temperatures.
In the case of industrial manufacture, in order to optimize the use of the injection molds, the preforms can be prepared outside the injection mold. In this case the preforms are frequently made rigid, for instance by a thermoplastic binder, in order to facilitate their positioning in the injection molds.
The production of the preform is a critical step in the R.T.M. process, particularly for complex shapes having strong concavities, as is true in the case of tire rims.
French Patent 2595621 proposes manufacturing a preform of revolution for a part of composite material by placing a fibrous texture with deformable meshes, whether woven or plaited, on a preforming matrix having a shape similar to that of the structure to be produced, so as to fit the shape of the preforming matrix by auto-adaptation of the meshes. The process consists in placing the fibrous texture on the preforming matrix at an axial end of said preforming matrix, with the meshes having sides of opposite inclination with respect to the axial direction of the structure, and then gradually placing the fibrous texture on the preforming matrix in the direction towards the other end, while subjecting the texture to a tension in this axial direction.
This process leads to a symmetrical orientation of the reinforcement fibers of a fabric relative to, the axial direction of the structure, which is not suitable in the case of tire rims, for which it is desirably to obtain a circumferential and axial orientation of the reinforcement fibers.
European Patent Application EP 0327173 presents a solution for the production of preforms of composite wheels by winding continuous fibers axially and then circumferentially. However, this process is slow and requires large and expensive equipment.